1. Field of the Invention
This invention relates to a camera having a focus detecting apparatus.
2. Related Background Art
Cameras provided with the focus detecting function have heretofore generally been of a construction in which a focus detecting optical system is disposed on the optic axis of a photo-taking lens or at a location somewhat deviated therefrom, but where an attempt has been made to add the spot photometering function to the camera, the following problem has been encountered. That is, it is necessary that the spot photometering optical system be also disposed substantially at the same location as the focus detecting optical system, namely, near the optic axis of the photo-taking lens, and therefore a contrivance such as dividing the optical path thereof by a half-mirror or the like has been required with a result that the construction becomes complicated and is disadvantageous in terms of the quantity of light.
There are also available cameras in which a spot photometering sensor or the like is disposed near the finder, but such cameras are of the type in which a light beam having passed the central split prism position of a focusing screen is photometered and therefore, it has been impossible to accomplish accurate photometry. It is also necessary to divide the optical path thereof by a half-mirror or the like in a manner similar to that described previously and therefore, such cameras have been disadvantageous in terms of both construction and quantity of light. Further, there has also been proposed a camera in which a sensor for focus detection is used also as a sensor for spot photometry (for example, Japanese Laid-Open Utility Model Application No. 96526/1983), but this camera has suffered from a problem that the photometering area is very small and much time is required for photographing because photometry and distance measurement must be done time-serially.
Also, in a single lens reflex camera, the provision of both the focus detecting function and the TTL flashlight controlling function involves considerable difficulties in layout because generally both of the optical systems therefor are disposed in the lower portion of a mirror box. That is, from the necessity of distance-measuring the center of the picture plane in the focus detecting optical system and from the necessity of equalizing the photometric sensitivity distribution at the left and right in the TTL flashlight controlling optical system, it is ideal to dispose the centers of the optical paths thereof on the center of the photo-taking optic axis, but for this purpose, a contrivance such as dividing the optical path by a beam splitter or the like is necessary, and this leads to the difficulty in making the camera compact as well as the disadvantage in terms of quantity of light and thus, it has been unavoidable either to sacrifice the performances of the respective devices from those limitations or to shift the TTL flashlight controlling optical system from the center of the photo-taking optic axis and sacrifice the photometric sensitivity distribution.